Manufacture of organolead compounds



United States Patent O MANUFACTURE OF ORGAN OLEAD COIVIPOUNDS Sidney M.Blitzer and Tillmon H. Pearson, Baton Rouge, La., assignors to EthylCorporation, New York, N. Y., a corporation of Delaware No Drawing.Application March 28, 1955 Serial No. 497,378

7 Claims. (Cl. 260-437) This invention relates to a process for themanufacture of organolead compounds. In particular, thisinvention isdirected to an improved process for the manufacture of tetraethyllead.

The process employed in present commercial, practice for the manufactureoftetraethyllead has been in use for a number of years and, in general,is satisfactory. However, it has certain disadvantages which areovercome by practicing our invention. It proceeds by reacting asodium-lead alloy, of composition controlled to correspond substantiallyto N-aPb, with ethyl chloride according to the following equation:

With the highest yields obtained thereby, only about 22 percent of thelead present in the NaPballoy is converted to tetraethyllead. Underconditions of best operation of this process, no one heretofore, as faras we are aware, has been able to increase this yield ,of tetraethylleadby even a few percent, due to the inherent limitation in yield as isapparent from the consideration of the above equation. It should benoted that in this reaction at least 75 percent of the lead originallyemployed is not alkylated. Thus, in this reaction, large quantities oflead must be recovered and reprocessed to NaPb alloy in order to make iteconomical. A further disadvantage of such a large quantity ofunreacted' lead is that valuable reaction space in the reaction vesselis occupied by materials which are essentially inert for the manufactureof tetraethyllead under present conditions and mode of operation.

Other processes for the production of .organolead compounds, and inparticular tetraethyllead, have been de-' vised to consume the leadproduced in the above equation. While such processes are satisfactoryfrom the standpoint of lead consumption, they sufier an additionaldrawback in common with the present commercial process in that theyrequire organo halide as the ethylating agent. One such process is thatdescribed in U. S. Patent 2,535,190 wherein lead as, for example, thatproduced in the commercial process, is treated with metallic .magnesiumand ethyl chloride in the presence of a catalyst preferably an alkylether. Thus, in this process as well as the present commercial process,the tetraethyllead manufacturing operation is restricted by thenecessary balance between the metallic sodium required and the organicchlorine in the ethyl chloride.

It is therefore an object of this invention to provide a process for themanufacture of organo'leadcompounds which overcomes the above objectionsto the present commercial process and those processes which have beenproposed more recently as an improvement thereover. Particularly, it isan object of the invention to increase the conversion of lead totetraethyllead above that obtained in present commercial practicewithout requiring the use of metallic sodium, metallic lead, or alkylhalogen compounds.

These and other objects of this invention are accom- Patented Nov. 4, 1958 plished by reacting .a lead halide wherein the halide has an atomicweight greater than 35, that is the chlorides, bromides, and iodides oflead, and mixed lead halides, with an organo metallic compound of groupIII A of the periodic table, that is boron, aluminum gallium, andindium, wherein the group III A.metal is the sole metal in the rnetalloorganic compound- In accordance with thisinvention, it has beendiscovered that to produce organole'ad compounds it is unnecessary tostart with a lead alloy, or in fact to em? ploy'metallic lead at all.Among the lead halides that can be employed in the process of thisinvention are lead chloride, lead'bromide, lead iodide, leadbromoiodide, lead chloroiodide, and lead chlorobromide.

The process of the present invention can best be understood byconsidering the-chemical equation involved. In general, the processproceeds according to the equation where R is an organic radical and Xis halogen having atomic weight greater than 35, and M represents ametal of group III A of the periodic table, namely boron, aluminum,gallium, or indium. In the preferred embodiment of this process theorganic radicals are hydrocarbons and particularly are non-aromatic oraromatic. Among the non-aromatic radicals we can employ alkyl orhydrocarbon substituted alkyl radicals. In general, we prefer the loweralkyl radicals having up to about eight carbon atoms. Among the aromaticradicals which can be employed in the above reaction are included phenyland hydrocarbon substituted phenyl radicals such as thealkaryl radicals.In general, aromatic radicals having up .to ten carbon atoms aresatisfactory. Thus, the compounds MR may be considered alkylating orarylating agents with re:

spect to the lead in the inorganic lead compound.

Of greatest current importance from a commercial standpoint. isthemanufacture of te'traethyllead by the process of .this invention.This embodiment can be illustrated by reference to the following.equation representing the.

preferred embodiment.

4AlEt +6PbCl PbEt +3Pbf+4AlCl t Illustrative of the a lkylating orarylating agents which we can employ are trimethyl aluminum, trimethylgallium, trimethyl boron, trimethyl indium, triethyl aluminum, triethylgallium, triethyl boron, triethyl indium, tripropyl aluminum, tripropylgallium, tripropyl boron, tripropyl indium, tributyl aluminum, tributylgallium, tributyl boron, tributyl indium, triamyl aluminum, .triamyl.

gallium, triamyl boron, triamyl indium, and the like up to abouttrioctyl aluminum, trioctyl gallium, trioctyl boron, trioctyl indium,triphenyl aluminum, triphenyl gallium, triphenyl boron, triphenylindium, tribenzyl aluminum,

tribenzyl gallium, tribenzyl boron, tribenzyl indium, tri-.

compounds can be employed to produce mixed organo- Such raw materialsinclude, for ex-' lead compounds. ample, dimethyl ethyl aluminum,dimethyl phenyl alumi num, dibutyl phenyl gallium, diphenyl methylboron, and the like.

By the process of this invention, as muchas SOpercent' of the lead inthe foregoing lead salts is directly converted to organolead, or inparticular, in a commercial embodia aaz ment, to tetraethyllead. Theremaining portion of the lead is in a highly active form as lead metaland is ideally suited for employment in the commercial process employingsodium-lead alloy or in that which proposes the reaction of metalliclead with an alkylating agent in the presence of magnesium and acatalyst. Conversely, the lead so produced by this invention can berecycled economically to the present process by conversion to theappropriate lead salt.

-Our invention is adaptable to the production of organolead compoundsgenerally, such as tetraethyllead, tetramethyllead, dimethyldiethyllead,tetraphenyllead, triethylphenyll'ead and tetrapropyllead. Nevertheless,for convenience in describing our invention hereafter,- specificreference will be made to tetraethyllead', the most widely known becauseof its use as an anti-knock agent. Whenever, in the followingdescription, this material is referred to, it is to be understood thatother organolead compounds or mixtures can be made by our process.

Likewise, aluminum triethylis the preferred organic reactant'in-theprocess of this invention and for convenience, sometimes hereinafter theinvention will be described with reference to the employment of aluminumtriethyl. However, when this material is referred to, 'it is to beunderstood that the other group III A metalscan be employed as themetallic organic reactant of this process. a

Generally, the process of this invention is conducted as follows. Into areaction vessel, preferably a stirred autoclave, is placed the desiredquantities of organo metallic compound, for example, an organo aluminumcompound, suspended or dissolved in an inert liquid carrier such as, forexample, a hydrocarbon-of medium boiling range. The appropriate leadsalt, for example lead chloride in finely divided solid form isintroduced through a hopper containing a plugcock into the autoclavewhile agitating to create a suspension of the lead compound in the inertliquid carrier. The connection to the hopper is thereupon closed andmoderate heat is applied to the reaction vessel while continuing theagitation. Thereupon, an exothermic reaction ensues and upon reachingthe desired reaction temperature, cooling is provided through a jacketin the autoclave. In contrast to other processes for the manufacture oftetraethyllead, when this invention is employed it is not necessary toprovide expensive and complex reflux equipment as, by proper choice ofthe carrier liquid, the reaction can be conducted in a closed system.Thus, tetraethyllead can be produced without the co-presence of ethylchloridein the closed vessel. This greatly facilitates control of thereaction 'and prevents the existence of an otherwise hazardousoperation. After completion of the reaction, the organoleadpompoundproduced is in solution in the carrier liquid and'the other products,namely the aluminum salt and metallic lead, can be removed byfiltrationand the organolead compound removed froni the carrier by distillation.

The operation described above can be varied and it is not intended thatthis invention be limited to the specific sequence of addition of-thereactants. For example, the organoaluminum compound. can be added to asuspension of finely divided lead halide with agitation. Othermodifications will be evident.

While the above operations Were discussed in connection with a batchoperation, they can be 'successfullly adapted to acontinuous process. Inaddition to applying the above operations to a continuous process, othermodifications of a continuous process can be made, such as first mixingtogether all the reaction materials and then passing them continuouslythrough a suitable reaction zone.

Ithas been indicated that the process of the present invention isconducted in the presence of an inert car-.

rier liquid. Hydrocarbons of appropriate boiling point with respect tothe organolead compound'produced are satisfactory and can be chosenso-asito providev a solution I of the product suitable for otherapplications or so that they can be readily removed by distillation at atemperature at which the organolead compound will not decompose. Otherinert carrier liquids are satisfactory and Where the product is a liquidsuch as, for example, in the manufacture of tetraethyllead, theorganolead compound itself can be employed as a carrier liquid. In suchan operation, economies are efiected by obviating the necessity ofrecovery by other means than merely filtration of the co-producedsolids. Another class of carrier liquids comprises the liquid amines,liquid ammonia,-and ethers. The principalcriterion of choice, therefore,of a carrier is the physical characteristic of the organolead compoundproduced, and the inertness of the liquid .to the organo aluminumreactant. Certain of the afore- :JTll'lOIled reactant carriers, whileinert to the reactants, exhibit a beneficial effect on the reactionwhich may be, considered catalytic in nature and contribute to the easeof reaction and rapidity of arriving at completion of'the reaction atrelatively lower temperatures and pressures.

In general, when conducting this'process in the presence of a liquidcarrier as above, the amount of carrier should be proportioned so as toprovide adequate heat removal facilities. In general, the load on theheat transfer medium is proportional to the concentration or relativeproportion of the reactants and carrier. In'a batch operation, it ispreferred to employ the liquid diluent in the proportion of as much as1,000 parts per part of organo metallic reactant. In a continuousoperation or in an operation provided the maximum heat transfer medium,a more concentrated reaction mixture can be employed wherein as littleas equal parts by weight of carrier and organo metallic reactant areemployed. In

general, it has been found that a more concentrated reaction mixtureprovides a rapid reaction and, provided adequate heat removal means areprovided, this is an ad-1 vantage as the organolead product is subjectedto the.

. elevated reaction temperature for the shortest practical.-

time, thereby minimizing thermal decomposition or undesirable sidereactions. I

It has been found that by increasing the ratio of. the organo aluminumreactant to solvent that, other condi-' tions remaining constant, theyield is significantly improved. Thus, when employing an aromaticsolvent, increasing the molar ratio of organo aluminum to solvent tenfold in the reaction with a lead halide, a 200 percent increase in yieldof organolead is obtained. Thus, by; increasing the molar ratio oforgano aluminum reactant to solvent from .01 to .05, the conversionbased upon lead halide is increased from 12 percent to 17 percent.Similarly, at a higher concentration a corresponding conver-" sionincrease is obtained.

While it has been found that in general any inert liquid which acts as asolvent for the organo aluminum com-, pound can be employed withgoodresults, generally su perior results are obtained when aromatichydrocarbon solvents are employed. Not only is a more rapid reactionencountered, but the ultimate yield is considerably improved incomparison, for example, to a parrafinic hydrocarbon solvent. Amongsuch'preferred aromatic. solvents are included benzene, toluene, xylene,and .the liquid alkyl naphthalenes such as a-methyl naphthalene,B-methyl naphthalene, ethyl naphthalene, tetralim and] the like. p l

The group III-A metallo organic compound employed in the process of thisinvention can be prepared by methods well known in the art. For example,reaction a between organo lithium compounds and aluminum halidesproduces the corresponding organo aluminum compound. Thus, aluminumtriethyl can be prepared by reaction be tween lithium ethyl and aluminumchloride. More recently, it has been proposed to produce organoalurninum compounds by reaction between aluminum hydride and,

the appropriate olefin. It is not intended, however, thatthe scope ofthis invention be limited to any particular method of producing "thehydrocarbonficarryingreactant;

This invention can .be'furtherunderstoodbyl the following detailedworking example of one method of practicing this invention as directedto the manufacture "of tetra ethyllead.

' Example-I An autoclave equipped with internal.agitation, externalheating means, and external cooling meansis employed having a hopperattached thereto for containing finely divided leadsalt. The hopper hasaplugcock at the discharge end for admis'sion'of the lead salt totheautoclave. To the autoclave are added 87 parts of toluene, agitation iscommenced and 3.9 parts of lead chloride of particle size of less thanA6 inc'h were admitted to the autoclave. The stop cock of the hopper wasclosed. The autoclave is purged with dry nitrogen .gas then 1.5 parts oftriethyl aluminum are fed thereto. The reaction mixture, while under anitrogen atmosphere, was maintained between 20 and 25 :C. for atotalreaction period of l/i hour. The mixture was then filtered'toremove solid constituents which are further processed for recovery oflead value. The filtrate was washed with an equal volume of water. Theorganic layer was transferred to a still for removal by vacuumdistillation of the toluene and recovery of the tetraethyllead from themixture. The conversi0n obtained was 46 percent of the theoretical.

Similarly, when trimethyl aluminum, tripropyl aluminum, triphenylaluminum, tribenzyl aluminum, triethyl aluminum, and tributyl aluminumare employed in the process of the foregoing example, satisfactoryyields of tetramethyllead, tetrapropyllead, tetraphenyllead,tetrabenzyllead, tetraethyllead, and tetrabutyllead are produced,respectively. Likewise, when trimethyl boron, tripropyl gallium,triphenyl indium, tribenzyl gallium, triethyl boron, and tributyl indiumare employed in the process of the foregoing example, satisfactoryyields of tetramethyllead, tetrapropyllead, tetraphenyllead,tetrabenzyllead, tetraethyllead, and tetrabutyllead are produced,respetcively.

In general, the reaction of this process is completed within arelativelyshort period at elevated temperatures, but a somewhat longer time isrequired at lower temperatures. In general, a reaction time of betweenabout onehalf to twenty hours is employed. In particular, in themanufacture of tetraethyllead with triethyl aluminum and lead bromide,we prefer to employ a reaction time of about ten hours or less.

The pressure employed in the reaction vessel is not critical and isusually the autogenous pressure created by the carrier liquid at thetemperature employed. Since organolead compounds are relatively toxic,it is desirable to employe a closed vessel in conducting this reactionwhich may create an elevated pressure if 'low boiling carrier liquidsare employed.

The temperature required in the operation of the process of thisinvention depends to a large degree upon the nature of the productsformed. It has been found that when elevated temperatures are employed,the alu minum halide produced in the reaction destroys the organoleadcompound produced at a rate competitive with the formation of theorganolead compound. There fore, in a batch operation wherein thecontact time is relatively extended, it is preferred to maintain thereaction temperature between about 10 C. to about 30 C. Within thisrange, variationis possible depending upon the stability of theorganolead compound produced, the degree of dilution by the inertdiluent, and duration of the reaction period. In a continuous operationwherein the reaction products can be rapidly removed from the reactionzone or wherein a quenching operation can be employed so as to rapidlyreduce the temperature of the reaction mixture or to destroy thealuminum halide prorluced, successful operation can be obtained withsome- 6 whathighertemperatures. ,Thus, if suchmeans are provided, theprocess can beconducted successfully in the temperature range of betweenabout 10 C. and 100 0. Conversely, in a batch operation, highertemperatures likewise be employed if provision is made for chemicallyremoving the aluminum halide produced from' the locus of the organoleadcompound. Thus, with the more stable organo'aluminum compounds, polar,solvents can be coemployed or complexing agents having atoms capable ofcoordinating with the aluminum halide produced can be successfullyemployed to provide successful reactions at more elevated temperatures.

While it was indicated above that, in general, a catalyst is notrequired for the practice of this invention, certain materials doexhibit a catalytic effect upon the reaction and, in many instances,their inclusion in the reaction provides a smoother operation. Typicalof such materials are heavy metal iodides as well as iodine itself,organic iodides, certain ketones such as acetone and methyl ethylketone, and ethers, amines, and aromatic solventsas in-' dicatedheretofore.

The following detailed examples serve to illustrate additional specificembodiments of the present invention. However, the invention is notintended to be limited thereto.

Example I] Following the procedure of Example I, with the exception thatthe autoclave was sealed after adding the reactants, 1.5 parts oftriethyl aluminum were reacted with 4.0 parts of lead bromide in 100parts of n-hexane. The temperature employed was to 89 C. and thereaction period was one hour. Based upon lead bromide converted toorganolead, a nearly quantitative yield of tetraethyllead was obtained.

Example III In a reactor maintained under an atmosphere of dry nitrogen,1.5 parts of triethyl aluminum were reacted with 3.91 parts of leadchloride in 200 parts of n-hexane. Room temperature was employed and aspontaneous reaction occurred. Tetraethyllead was recovered in highyield.

Example IV Tetrahexyllead is prepared in high yield by reacting trihexylaluminum with lead chloride in essentially stoichiometric amounts in thepresence of cyclohexane at atmospheric pressure and at a temperature of75 to C. for three hours reaction time.

Example V Again employing the procedure of Example I, tetraphenyllead isobtained in high yield when triphenyl aluminum dissolved in benzene isreacted with lead chloride in essentially stoichiometric quantities. Thetemperature employed is 75 to 83 C. for a period of 5% hours.

Example VI Example I is repeated essentially as described with theexception that tetraethyllead is employed as the diluent and thereaction temperature is 30 to 40 C. In this instance, the process isconducted continuously by continuously feeding the triethyl aluminum andlead chloride to the reactor and withdrawing a slurry of solids intetraethyllead from the reactor leaving a heel of tetraethylleadsuflicient to maintain fluidity of the reaction mixture.

Equally good results are obtained when the corresponding and otherorgano compounds of gallium, boron and indium are employed in the aboveexamples. For example, triethyl gallium, indium or boron can be reactedwith lead chloride to produce tetraethyllead. Triphenyl gallium, indiumor boron, preferably dissolvedin a suitable solvent such as benzene canbe reacted with lead bromide to produce tetraphenyllead. Other exampleswill be evi' dent.

driding to produce the corresponding aluminum hydride as thefirst stage.A second stage then comprises reacting said hydride with ethylenepreferably in thepresence of a solvent suitable as a carrier for theethyl aluminum, which is thereafter reacted with the lead chloride inaccordance with the foregoing descriptionof the present invention.pweclaim:

' '1. A process for the manufacture of hydrocarbon lead Compounds whichcomprises reacting a hydrocarbon metallic group .IH.-A I compoundwherein each hydrocarbon radical has up to about IOcarbon atomsinclusiveand is Selected fromthe'group consisting of alkyl and aryl radicals witha lead halide of a halogen selected from the group consisting ofchlorine, bromine and iodine. V 2. A processfor making alkylleadcompounds .which comprises reacting a lead halide of a halogen selectedfrom the group consisting of chlorine, bromine, and Eiodine with ,a:trialkyl aluminum compound wherein each: alkyl radical contains .upto.8 carbon atoms inclusive; H

v; '3.- .A proce'ssjfor the 'tmanufacturelof.'tetraethyllead whichComprises reactinglead Tchloride with :triethyl alu, minum.

4. The process of claim S Wherein the reaction is com ducted in thepresence of an inert carrier liquid. 5. The-processof claim 3lwhereinthe reaction is con ducted at-a temperature between about -10 to 100? C.i

6. The p'rocess of claim 5 wherein the reaction is conducted in thepresence of'an inert carrier liquid. 7. The process of claimS'whereinsaid carrier liquidis toluene. ,1. v

: References Cited in the file of this patent UNITED STATES PATENTS v vp Ziegleret a1. r Mar. 26, 1957;

' OTHER REFERENCES Leeperet al. Chem. Revs. 54, 108 (1954) citing Austinet al. J. A. C'. S. 54, 3726 (1932).;

1. A PROCESS FOR THE MANUFACTURE OF HYDROCARBON LEAD COMPOUNDS WHICHCOMPRISES REACTING A HYDROCARBON METALLIC GROUP III-A COMPOUND WHEREINEACH HYDROCARBON RADICAL HAS UP TO ABOUT 10 CARBON ATOMS INCLUSIVE ANDIS SELECTED FROM THE GROUP CONSISTING OF ALKYL AND ARYL RADICALS WITH ALEAD HALIDE OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF CHLORINE,BROMINE AND IODINE.